Pressure switch



Nov. 19, 1968 c, A, SCHAD 3,412,223

PRESSURE SWITCH Filed Aug. 1, 1966 SET 58 g u RU 2Q Q \1 56 48 7 3% h 52 Q RESET r -22 p PRESSURE t 50 6 J F. 3.2. S0- P Q k /a E SET 52 8 3 l 0) 5 RESET PRESSURE INVENTOR. CHARLES A. SCHAD ATTORNEYS United States Patent 3,412,223 PRESSURE SWITCH Charles A. Schad, 6720 E. 25th Place, Tulsa, Okla. 74129 Filed Aug. 1, 1966, Ser. No. 569,177 7 Claims. (Cl. 20083) This invention relates to a pressure switch. More particularly, and as a primary object, this invention provides a pressure switch which is adaptable to operate under conditions of slow rates of change of the pressure which is being applied to the switch.

In those particular instances where pressure switches are utilized for control, i.e., to start or stop pumps or to open or close valves, as a function of the fluid level in the tank and wherein the level changes relatively slowly, problems arise especially when linear responsive pressure switches are utilized. By a linear responsive switch is meant apparatus wherein a piston or diaphragm displacement is a linear function relative to the applied hydrostatic or other pressure which actuates, for example, a typical single pole-double throw mercury capsule switch element. Often the mercury, during certain pressure situations, will balance in the middle of a tube prior to its complete switching operation. During such an interval switching logic is lost since a pump may be signaled both to run and/ or to stop or other harmful situations may occur. Accordingly, it is an object of this invention to overcome problems associated with conventional pressure switches.

These and other objects of the invention will become more apparent upon further reading of the specification and claims when taken in conjunction with the following illustrations of which:

FIGURE 1 is a sectional view of the switch embodied in this invention.

FIGURE 2 is a graphic diagram of the operation of a conventional linear responsive switch.

FIGURE 3 is a graphic diagram of the operation of the switch embodied in this invention.

Referring first to FIGURE 2, a conventional pressure switch produces substantially a linear piston displacement relative to the applied pressure with the limit switching points designated as reset and set for a desired pressure relationship. Where liquid level indication, as within a tank, is desired a switch of this nature is adaptable but where the primary function is a form of control over pumps, motors, valves or the like, then a quasi-step responsive switch of the type described herein and diagrammatically shown in FIGURE 3 is desired. As such, it is shown that there is a point reached betwen the reset and the set pressures relative to a given piston displacement wherein the piston displacement is relatively zero, i.e. there is no relative movement whatsoever until a given pressure is reached. As such action is achieved by the switch without interference from intermediate positions of piston displacement where the switch may oscillate between a conductive and non-conductive situation. Hence, the effect achieved by this invention is that amplification of the piston displacement versus pressure occurs in the area of desired control permitting the use of much smaller pressure diaphragms and a compact switch.

Referring now to the switch described in FIGURE 1, a diaphragm retainer includes installation connection means such as threads 12 wherein communication with the pressure source is provided by inlet pressure port 14. The retainer is adapted to hold and seal diaphragm 16 relative to main switch housing 18. The remainder of the outer switch housing includes cover mounting 20 and protective cover cap 22 threaded to the former. Diaphragm retainer 10 is held to main switch housing 18 by a plurality of circumferentially spaced bolts 24 while cover 20 is retained thereto by mounting bolts 26. Internally a control mechanism such as a conventional microswitch 30, as for example the set-reset type, is mounted to housing 18. The reset button is identified by numeral 32 while the set button is identified as 34. The switch is mounted with appropriate electrical leads which are adapted to extend outwardly of switch housing 18 through opening 36. Diaphragm actuated member or piston 38 extends around the switch 30 and includes a set pin adjustable contacts 40- positioned relative to set pin 34. At the upper end of piston 38 a shoulder 42 is adapted to be abuttable against the under side lip abutment 44 formed as a part of the axial opening in mounting 20. On the upper side, lip abutment 46 acts to restrain the downward movement of high pressured piston 48 above'which spring 50 operates between an adjustment sleeve 52 tending to bias the piston downwardly against the upper side of abutment 46. A low pressure interlock system with piston 38 is provided by means of spring 54 operating against the upper side of piston 38, the adjustment thereof being accomplished by bushing 56 and threaded tension adjustment member 58 which are a part of the high pressure piston 48. A reset contact member 60 is threadably adjustable within the upper part of piston 38 relative to reset button 32 of the switch 30. The member further acts as a guide for spring 54 and bushing 56 as well as high pressure piston 48.

In operation of the switch, pressure applied through port 14 operates against diaphragm 16 moving piston 38 upward relative to microswitch 30 which is in a reset position. The piston traveling upward with increasing pressure abuts high pressure piston 48. High pressure spring adjustment sleeve 52 has been previously adjusted to preload high pressure piston 48 to a desired pressure condition. The piston and diaphragm remain at a substantially static condition until the pressure in the port 14 exceeds the preload pressure condition whereupon piston 38 moves upward again lifting the high pressure piston 48 until a point is reached where set pin 34 is actuated which by appropriate electrical connection operates a particular desired control mechanism. As the input pressure falls, high pressure piston 48 returns until seated against the upper side of abutment 46 where further movement is halted. The reset contact member 60 has been previously adjusted such that reset of the switch 30 does not occur during these intermediate pressure conditions. As the pressure continues to drop and by reason of low pressure interlock adjustment 58 preloading against the upper side of piston 38, the reset button is actuated only at the desired low pressure resetting. Hence, it could be seen that there is a condition existing between the actual set and resetting positions of microswitch 30 wherein the actual piston displacement is substantially halted preventing oscillation of the switch. Referring to FIGURE 3 it should be understood that the slope of the steps may be varied by selecting springs 50 and 54 of desired force versus displacement constants. The step starting points are determined by the preloading adjustments using members 52 and 58. It should be readily understood that small displacement errors due to expansion, contraction or wear will result in a much smaller corresponding shift in the controlled pressure or level.

The invention has been described with reference to specific or preferred embodiments. It would be apparent, however, that other modifications can be made without departing from the spirit and scope of the invention. For example, although this invention has been specific to a microswitch of the type shown and described, generally any type of "maintain-contact-type switch is applicable and preferred. In addition, it is possible to replace the electrical control valve or switch with a pneumatic control valve for instruments actuatable by pressure fluid. Accordingly, this invention should be construed not to be limited to the embodiment herein described but should be limited only by the scope of the appended claims.

What is claimed:

1. A step responsive fluid pressure switch setting and resetting actuating mechanism comprising, in combination:

a housing including means to attach said switch thereto;

a fluid pressure actuated piston movable relative to said housing and said switch so as to set or reset said switch at a point of travel in one direction of movement and reset or set, respectively, said switch at a point of travel in the other direction of movement;

a high pressure piston movable, after contact with said pressure actuated piston during one direction of movement, against a first predetermined spring force; and

a second low pressure predetermined spring force means operable between said high pressure piston and said pressure actuated piston when said pressure is below said first predetermined spring force.

2. A mechanism according to claim 1 including a diaphragm retained between said fluid pressure and said pressure actuated piston.

3. A mechanism according to claim 1 including adjustable contacts on said pressure actuated piston for actuation of said switch set and reset mechanism.

4. A mechanism according to claim 1 including means on said housing to adjust said first spring force to a predetermined value.

5. A mechanism according to claim 1 including means on said high pressure piston to adjust said second low pressure spring force to a predetermined value.

6. A mechanism according to claim 1 including:

a diaphragm retained between said fluid pressure and said pressure actuated piston;

adjustable contacts on said pressure actuated piston for actuation of said switch set and reset mechanism;

means on said housing to adjust said first spring force to a predetermined value; and

means on said high pressure piston to adjust said second low pressure spring force to a predetermined value.

7. A step responsive fluid pressure setting and resetting actuating mechanism for electrical or pneumatic control valves comprising the combination of:

a housing including means to attach said control valve thereto;

a fluid pressure actuated piston reciprocatably movable relative to said housing and said control valve so as to set or reset said valve at a point of travel in one direction of movement and reset or set, respectively, said valve at a point of travel in the other direction of movement;

a high pressure piston movable, after contact with said pressure actuated piston during one direction of movement, against a first predetermined spring force; and

a second low pressure predetermined spring force means operable between said high pressure piston and said pressure actuated piston when said pressure is below said first predetermined spring force.

References Cited UNITED STATES PATENTS 1,781,289 11/1930 Levy ZOO-83.5 2,304,400 12/1942 Eaton 200--67 2,395,007 2/1946 Leupold 200-8391 2,779,838 1/1957 Reis 200153.19 XR 2,800,549 7/ 1957 Guthrie 200-83.91

ROBERT K. SCHAEFER, Primary Examiner.

H. BURKS, Assistant Examiner. 

1. A STEP RESPONSIVE FLUID PRESSURE SWITCH SETTING AND RESETTING ACTUATING MECHANISM COMPRISING, IN COMBINATION: A HOUSING INCLUDING MEANS TO ATTACH SAID SWITCH THERETO; A FLUID PRESSURE ACTUATED PISTON MOVABLE RELATIVE TO SAID HOUSING AND SAID SWITCH SO AS TO SET OR RESET SAID SWITCH AT A POINT OF TRAVEL IN ONE DIRECTION OF MOVEMENT AND RESET OR SET, RESPECTIVELY, SAID SWITCH AT A POINT OF TRAVEL IN THE OTHER DIRECTION OF MOVEMENT; A HIGH PRESSURE PISTON MOVABLE, AFTER CONTACT WITH SAID PRESSURE ACTUATED PISTON DURING ONE DIRECTION OF MOVEMENT, AGAINST A FIRST PREDETERMINED SPRING FORCE; AND A SECOND LOW PRESSURE PREDETERMINED SPRING FORCE MEANS OPERABLE BETWEEN SAID HIGH PRESSURE PISTON AND SAID PRESSURE ACTUATED PISTON WHEN SAID PRESSURE IS BELOW SAID FIRST PREDETERMINED SPRING FORCE. 